Myself I would just turn of the minification then you can easily find the specific css and you can fairly quickly determine which file it is coming from by looking at the list of files in style.config (the css files are combined in the same order that they are listed in style.config) and opening the separate css files.

Keep in mind that turning off caching doesn't work if the files are loaded separately as static resources, the browser will cache them, the only time we have control over caching is when we have them combined by the css handler.

Best,

Joe